1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having a latching means capable of scanning.
2. Description of the Related Art
In synchronous semiconductor integrated circuits which have been more and more complicated, the recent most popular technique is to use a latching circuit (scan chain) capable of scanning to test this latching circuit by separating only a certain function, thereby greatly reducing the test time. The latching means (scan chain) capable of scanning is a means in which a plurality of registers and the like are connected into one or a plurality of chains so that data stored in a preceding register can be shifted (scanned) to a succeeding register.
In particular, a macro cell for forming an embedded memory containing both a memory circuit and logic circuit has a large number of input/output terminals. Hence, it is essential to include the scanning function as described above to improve the fault detection ratio of the whole semiconductor integrated circuit (semiconductor chip).
FIG. 1 is a schematic view showing a method of realizing scan in a conventional macro cell. This macro cell 101 is for forming an embedded memory or the like. As shown in FIG. 1, the macro cell 101 has a large number of input/output terminals (to be referred to as IO terminals hereinafter) 102, so these IO terminals 102 are arranged with a spatial extension. Each IO terminal 102 has an input/output register (to be referred to as an IO register hereinafter) 103. These IO registers 103 have a scanning function to test data (an external path) input from the outside of this macro cell, and are connected in series.
A scan input terminal 104 is connected to one end of these IO registers 103. A scan output terminal 105 is connected to the other end of the IO registers 103. Data SI to be scanned is input to the input terminal 104, and scanned data SO is output from the scan output terminal 105. Although not shown, scan is executed by using a control input signal and a clock signal in addition to these data.
FIG. 2 is a view showing the arrangement of a conventional embedded memory macro. An example of the realization of scan in this embedded memory macro will be described below.
As shown in FIG. 2, this embedded memory macro 111 has the macro cell 101 shown in FIG. 1, an operation control circuit 112, and a macro cell 101B. This macro cell 101B is the mirror inversion of the macro cell 101 with respect to the operation control circuit 112. In an embedded memory macro, to increase the memory capacity and share the operation control circuit 112, the macro cells 101 and 101B are usually so arranged as to have a mirror inversion relationship on the two sides of the operation control circuit 112.
In each of the macro cells 101 and 101B, 128 IO registers and 128 IO terminals are arranged. At the right end of the macro cell 101, a scan input terminal 104 connected to the right end of the IO registers is formed. At the left end of the macro cell 101, a scan output terminal 105 connected to the left end of the IO registers is formed.
The operation control circuit 112 has an input/output line for inputting and outputting a control signal CNT and has a register for storing this control signal CNT. At the right end of the operation control circuit 112, a scan input terminal 113 connected to the register is formed. At the lower end of the operation control circuit 112, a scan output terminal 114 connected to the register is formed.
At the left end of the macro cell 101B, a scan input terminal 104B connected to the left end of the IO registers is formed. At the right end of the macro cell 101B, a scan output terminal 105B connected to the right end of the IO registers is formed. In addition, the scan output terminal 114 and the scan input terminal 104B are connected by a line 115.
The memory macro 111 configured as shown in FIG. 2 can achieve a memory macro scanning function by inputting data SI to be scanned to the scan input terminal 104 at the right end, and outputting scanned data SO from the scan output terminal 105B.
Unfortunately, the line 115 between the scan output terminal 114 and the scan input terminal 104B is a long line extending over the 128 IO terminals, and therefore deteriorates the performance of the scan operation. Also, this line 115 must be formed outside the memory macro. This interferes with automatization of the scan operation.